﻿namespace ACadSharp.IO.DWG
{
	internal class CRC
	{
		/// <summary>
		/// Standard 8 bit CRC calculation.
		/// </summary>
		public static readonly ushort[] CrcTable = new ushort[256]
		{
			0x0000,0xC0C1,0xC181,0x0140,0xC301,0x03C0,0x0280,0xC241,
			0xC601,0x06C0,0x0780,0xC741,0x0500,0xC5C1,0xC481,0x0440,
			0xCC01,0x0CC0,0x0D80,0xCD41,0x0F00,0xCFC1,0xCE81,0x0E40,
			0x0A00,0xCAC1,0xCB81,0x0B40,0xC901,0x09C0,0x0880,0xC841,
			0xD801,0x18C0,0x1980,0xD941,0x1B00,0xDBC1,0xDA81,0x1A40,
			0x1E00,0xDEC1,0xDF81,0x1F40,0xDD01,0x1DC0,0x1C80,0xDC41,
			0x1400,0xD4C1,0xD581,0x1540,0xD701,0x17C0,0x1680,0xD641,
			0xD201,0x12C0,0x1380,0xD341,0x1100,0xD1C1,0xD081,0x1040,
			0xF001,0x30C0,0x3180,0xF141,0x3300,0xF3C1,0xF281,0x3240,
			0x3600,0xF6C1,0xF781,0x3740,0xF501,0x35C0,0x3480,0xF441,
			0x3C00,0xFCC1,0xFD81,0x3D40,0xFF01,0x3FC0,0x3E80,0xFE41,
			0xFA01,0x3AC0,0x3B80,0xFB41,0x3900,0xF9C1,0xF881,0x3840,
			0x2800,0xE8C1,0xE981,0x2940,0xEB01,0x2BC0,0x2A80,0xEA41,
			0xEE01,0x2EC0,0x2F80,0xEF41,0x2D00,0xEDC1,0xEC81,0x2C40,
			0xE401,0x24C0,0x2580,0xE541,0x2700,0xE7C1,0xE681,0x2640,
			0x2200,0xE2C1,0xE381,0x2340,0xE101,0x21C0,0x2080,0xE041,
			0xA001,0x60C0,0x6180,0xA141,0x6300,0xA3C1,0xA281,0x6240,
			0x6600,0xA6C1,0xA781,0x6740,0xA501,0x65C0,0x6480,0xA441,
			0x6C00,0xACC1,0xAD81,0x6D40,0xAF01,0x6FC0,0x6E80,0xAE41,
			0xAA01,0x6AC0,0x6B80,0xAB41,0x6900,0xA9C1,0xA881,0x6840,
			0x7800,0xB8C1,0xB981,0x7940,0xBB01,0x7BC0,0x7A80,0xBA41,
			0xBE01,0x7EC0,0x7F80,0xBF41,0x7D00,0xBDC1,0xBC81,0x7C40,
			0xB401,0x74C0,0x7580,0xB541,0x7700,0xB7C1,0xB681,0x7640,
			0x7200,0xB2C1,0xB381,0x7340,0xB101,0x71C0,0x7080,0xB041,
			0x5000,0x90C1,0x9181,0x5140,0x9301,0x53C0,0x5280,0x9241,
			0x9601,0x56C0,0x5780,0x9741,0x5500,0x95C1,0x9481,0x5440,
			0x9C01,0x5CC0,0x5D80,0x9D41,0x5F00,0x9FC1,0x9E81,0x5E40,
			0x5A00,0x9AC1,0x9B81,0x5B40,0x9901,0x59C0,0x5880,0x9841,
			0x8801,0x48C0,0x4980,0x8941,0x4B00,0x8BC1,0x8A81,0x4A40,
			0x4E00,0x8EC1,0x8F81,0x4F40,0x8D01,0x4DC0,0x4C80,0x8C41,
			0x4400,0x84C1,0x8581,0x4540,0x8701,0x47C0,0x4680,0x8641,
			0x8201,0x42C0,0x4380,0x8341,0x4100,0x81C1,0x8081,0x4040 
		};

		/// <summary>
		/// CRC lookup table containing 256 32-bit values.
		/// </summary>
		public static readonly uint[] Crc32Table = new uint[]
		{
			0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,
			0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
			0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
			0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
			0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
			0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
			0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
			0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
			0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
			0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
			0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,
			0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
			0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,
			0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
			0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
			0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
			0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,
			0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
			0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,
			0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
			0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
			0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
			0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,
			0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
			0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
			0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
			0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
			0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
			0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
			0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
			0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,
			0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
			0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
			0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
			0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
			0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
			0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,
			0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
			0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
			0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
			0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,
			0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
			0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,
			0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
			0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
			0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
			0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,
			0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
			0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
			0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
			0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
			0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
			0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,
			0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
			0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
			0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
			0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
			0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
			0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
			0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
			0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,
			0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
			0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
			0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d 
		};
		
		public static ushort ApplyCrc8(ushort dx, byte[] arr)
		{
			ushort retval = dx;
			for (int i = 0; i < arr.Length; ++i)
			{
				byte al = (byte)(arr[i] ^ (uint)(byte)(retval & (uint)byte.MaxValue));
				retval = (ushort)((ushort)(retval >> 8 & byte.MaxValue) ^ (uint)CrcTable[al & byte.MaxValue]);
			}
			return retval;
		}
	}
}
